1. Field of the Invention
The present invention relates to a single-lens-reflex digital camera, more specifically to a single-lens-reflex digital camera which is designed and configured to allow the photographer to see an optical image and a live digital image of an object to be photographed, so as to be selectively viewed through a viewfinder.
2. Description of the Prior Art
Typical SLR (single-lens-reflex) digital cameras are provided with a main mirror (quick-return mirror) positioned on an optical axis of a photographing lens so that light of an object which is passed through the photographing lens is reflected by the main mirror to be formed on a focusing screen as an optical image of the object. This optical image formed on the focusing screen is viewed through a viewfinder (viewfinder optical system). When the main mirror has been retracted from an optical path of the photographing lens, i.e., when the main mirror has risen, the light of an object which is passed through the photographing lens is formed on an image pickup device while an image signal of the object is visually indicated on an external LCD (liquid crystal display) monitor, or the like, to be viewed as a live digital image. Accordingly, in this type of digital camera, if the photographer desires to continue observing an object to be photographed through the digital camera, they have only two ways of viewing: they observe either an optical image of the object through the viewfinder or a live digital image of the object which is displayed on the external LCD monitor when the main mirror rises.
In view of this type of digital camera, a technology that installs a small LCD monitor in a viewfinder optical system to enable the photographer to observe a live digital image of an object, which is taken by an image pickup device and displayed on an external LCD monitor, through the viewfinder has been proposed in Japanese unexamined patent publication H10-294888 (hereinafter referred to as a first publication). According to this technology, the photographer can selectively observe the optical image and the live digital image through the viewfinder, which is effective for enhancing the convenience of the digital camera at a time of exposure.
In SLR digital cameras, to enable the photographer to view an optical image of an object and various information (e.g., an f-number and a shutter speed) at the same time, the viewfinder is provided therein with a display device for making the various information display on the focusing screen as visual information. An LCD is used as such a display device. Visual information displayed on the LCD is formed either on the focusing screen or at a position on an optical axis which is optically equivalent to the position of the focusing screen by an optical device. In Japanese unexamined patent publication 2000-137268 (hereinafter referred to as a second publication), a device for displaying a required image on the focusing screen using an EL (electroluminescent) display instead of such a type of LCD has been proposed. Specifically, forming an EL display in a peripheral part of the object image forming area (picture area) of the focusing screen and making the EL display indicate various information by making an EL drive circuit drive the EL display makes it possible to display the various information on the focusing screen together with an optical image of an object so that the photographer can view the various information and the optical image of the object at the same time through the viewfinder. Additionally, in the second publication, an arrangement wherein an EL display is formed on a surface of a prism serving as an element of a viewfinder optical system has also been proposed.
In the first publication, to allow the photographer to selectively view an optical image and a live digital image of an object, a movable mirror or the like which is installed in a part of a viewfinder optical system is driven to switch between two optical paths, and accordingly, the digital camera has to be provided with a drive mechanism for switching between the two optical paths, which complicates the structure of the viewfinder. Additionally, there is a problem of the viewfinder becoming large because an LCD monitor (internal LCD monitor) is installed in the viewfinder. Additionally, in the second publication, although the EL display mounted to the focusing screen can be made thinner than an LCD, this EL display displays only visual information, and accordingly, an image to be displayed on the focusing screen is limited solely to an optical image which is formed on the focusing screen via a photographing lens. On this account, to visually check the live digital image, the photographer has no other choice but to visually check the live digital image displayed on the external LCD monitor installed in the viewfinder, so that the viewfinder only has a capability similar to the viewfinder of a conventional SLR camera in the second publication.